The impact of frequency aliasing on spectral method of measuring T wave alternans

Di-Hu Chen, Sheng Yang

Department of Precision Machinery & Instrumentation, University of Science and Technology of China, Hefei 230027, China..

DOI: 10.4236/jbise.2009.22019                

Abstract

In this paper we investigate frequency aliasing in spectral method of measuring T wave alter-nans, which may lead a high false positive rate. Microvolt T wave alternans(TWA) has been evaluated as a means of predicting occurrence of ventricular tachyarrhythmia events and its association with the genesis of ventricular ar-rhythmias has been demonstrated. Nowadays, spectral method is one of the most widely used procedures for measurement of microvolt TWA. In our study, based on the sampling theory, the alternans frequency 0.5 cycles/beat, at which the power of the spectrum is used to calculated the Valt and K score (these two parameters indicate the TWA), is equal to the nyquist frequency. Thus this generates frequency aliasing which will make the power at the alternans frequency (P0.5) be two times of the real magnitude of the original spectrum amplitude. With the assump-tion that the noise spectrum follows the normal distribution, in spectral method of measuring T wave alternans, the measuring standard K score>3 to consider the T wave alternans sig-nificant is only with a p<0.133. By change the standard to K score>6 can solve this problem and make the p value to p<0.0027.

Keywords

TWA, Sampling, Spectral method, Frequency Aliasing

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	A. Bay& and J. Guindo, (1989) Sudden Cardiac Death. Spain: MCR.
[2]	J. P. Martinez, S. Olmos and P. Laguna, (2000) Simulation Study and Performance Evaluation ofT-Wave Alternans Detec-tor. Proceedings of the 22nd Annual EMBS International Con-ference, July 23-28, Chicago IL.
[3]	J. P. Martínez and S. Olmos, (2005) Methodological Principles of T Wave Alternans Analysis: A Unified Framework. IEEE Transactions On Biomedical Engineering, vol. 52, NO. 4.
[4]	B. D. Nearing, R. L. Verrier. (2002) Modified moving average method for T-wave alternans analysis with high accuracy to pre-dict ventricular fibrillation. J Appl Physiol, 92, 541-49.
[5]	D. R. Adam, J. M. Smith, S. Akselrod, S. Nyberg, A. O. Powell, R. J. Cohen. (1984) Fluctuations in T-wave morphology and susceptibility to ventricular fibrillation. J Electrocardiol, 17, 209–18.
[6]	A. L. Ritzenberg, D. R. Adam, R. J. Cohen. (1984) Period multi-plying-evidence for nonlinear behavior of the canine heart. Na-ture, 307, 159– 61.
[7]	J. M. Smith, E. A. Clancy, C. R. Valeri, J. N. Ruskin, R. J. Cohen. (1988) Electricalalternans and cardiac electrical instabil-ity. Circulation, 77, 110– 21.
[8]	D. M. Bloomfield, S. H. Hohnloser, R. J. Cohen. (2002) Inter-pretation and classification of microvolt T-wave alternans tests. J Cardiovasc Electrophysiol, 13:502– 12.
[9]	C. L. Phillips, J. M. Parr and E. A. Riskin. (2004) Signal, System and Transform. China Machine Press, Beijing.